Interlock is a non-profit organization that provides space for its members and the local community to develop and share their interests in science, technology, art, and culture.

Beaglebone Black PMIC for battery backup

One of my Interlock projects has been to explore the capabilities of the Beaglebone Black’s built-in Power Management Integrated Circuit (PMIC) that gives the BBB a pretty useful feature; charging and operating off of li-po batteries. If you look at the BBB board, you will see 4 through-holes behind the 5v plug. These are break outs for the PMIC and can be used to hook up to a battery.

beaglebone with sparkfun battery

Having a battery connected to your board gives you the ability to do things like making a UPS for you beaglebone so in the case of a power loss, it can politely shut-down, run a custom command, or just continue running for as long as the battery can charge it.bbb_pinouts


In most of the use cases, you’re going to find a lithium polymer that can produce around 3.7V which is under the BBB’s 5v requirement. 3.7V will work fine to power the board but of course your 5V USB port will not work while on the battery. Sparkfun has a few nice ones that have the voltage protection circuits built in to help limit the risk you brick your li-po.


There are 4 pins we’re talking about:bbb-batt-srm

  • TP5
  • TP6
  • TP7
  • TP8

You can see in the diagram what each pin-out is. Li-po’s are riskier than some batteries because they’re known to explode in some cases of over powering. A temperature sensor that is designed to check how hot the battery is getting and decide how to handle it, is built into the PMIC in case your battery doesn’t have this capability already(many do). The directions below are going to show you how to jump this temperatur check with a 10k resistor, which is not recommended if you value your home or hackerspace. If you don’t trust the battery you’re charging, I’d suggest looking into accurately reading the temperature from your battery. My Sparkfun batteries do no break out the temperature sensor so this wasn’t plausible.


  • jumper pins TP5 to TP6 (or use an SMT zero ohm resistor)
  • connect a 10K resistor between TP7 and TP8
  • Install a JST connector on TP6 and TP8
  • Connect your battery into the JST connector

With a little luck and the correct battery, you should be in business. You’ll need to let your battery charge before you try and yank the power cable from it. In the mean time, you can query the status of the battery via the i2cget command built into the OS.


The PMIC is accessible using I2C and the builti-n OS for BBB has a simple command line interface to query its state. The following command will tell you whether or not battery is plugged in:

i2cget -y -f 0 0x24 0xA

This will return information that contains this:

0 device 0x24
On battery power only? 0
STATUS: r[0xa]=0x88
Push Button = 0
USB Power = 0
AC Power = 1
CHARGER: r[0x3]=0x1
Active (charging) = 1

“Active” refers to whether it can recognize the battery you have plugged in.  You can also read this state to detect a power failure and automatically failover. If you’re using the default OS for the Beaglebone Black (the one that comes pre-installed), the OS will automatically shut itself down in the case of a power loss. You’ll want to either install another OS, or disable that service if you’d like to change how long the battery should stay online.

More info

A decent amount of research went into this simple project. There are a ton of warnings and caveats that I’m not going to cram into this blog post (i2c address is read only, pin-outs are not a standard size, beware of jumping the resistor next to the pins). You can find out more information here:

Thanks to Alex for finding a fatal flaw in the 10k resistor I was using.

from on March 2nd, 2015Comments0 Comments

Software Defined Radio Workshops

This Thursday the 19th, we have another installment of the Software Defined Radio (SDR) workshop. The goal of which is to provide introductory support to people learning about SDR’s as well as let some of the more seasoned folk work on their projects. We’ve talk to a lot of people lately about what an SDR is and why we have a workshop for it so I thought I’d review why they’re fun.

What is an SDR?

Unlike some radio equipment which only provides a small range of frequencies you can transmit and receive on, SDR’s let you use a single device, and control their frequency from very low (<100Mhz) to very high (2.4GHz+).


So what?

In the past, if you wanted to listen in on a certain frequency, say your garage door opener for example, you’d have to buy a piece of hardware that runs at that frequency — in this case it’s often 434MHz. Now for as little as $20, you can buy a device that can read your garage door opener at 433Mhz, listen to the local FM radio station at 90.5Mhz, or track airplanes at 1090Mhz. This lets you play with different frequencies and see what’s being transmitted. You may be surprised.

This also lets you learn about the basics of RF: electronics, antennas, ways to decode a signal.

The workshop is open to the public; non-members are welcome as always. Feel free to drop a comment on the meetup page if you’re interested but have some questions.

SDR Workshop on Meetup


from on February 17th, 2015Comments0 Comments

Interlock goes to Iceland to meet Hakkavélin

When we travel, it’s common for hackerspace members to reach out to other hackerspaces located in our destinations. It’s a great way to meet the locals, share ideas, and learn how other people run a hackerspace. Interlock has entertained guests from all over. Sometimes travelers will email us saying they are doing a tour of hackerspaces in the region and wanted to stop in for a night. When we’re available, we’re happy to entertain at the space and even take them out for a drink. I remember one visit from a group travelling first to New York City (NYC Resistor, Alpha One Labs), going up through Syracuse (SIG 315), to Rochester (Interlock) and ending up in Toronto (Hacklab). Our members have visited spaces all over the country; Florida, Texas, California, North Carolina, and Washington DC are a few that I can remember. There is even a hackerspace passport that Noisebridge started where you can get it stamped at the various hackerspaces that you visit.


Myself and another member recently visited Iceland for New Years for just over a week and the day after we landed, we jumped on the Hakkavélin IRC channel to reach out to see when open hours were and if we could arrange a visit. While the space wasn’t opened due to the holidays, Sigurður óskarsson was kind enough to meet us at the hackerspace to take us out to a cafe in town. We talked shop a bit, discussing projects people were working on and history of each others’ spaces, along with operational details like how they handled membership and how much they charged.

We learned about their door system which consisted of a full computer sitting outside of the space controlling the door lock. In order to get in, you have to figure out how to use the console in a hackery way. As I understand it, there’s also an IRC bot which controls this door if you message the right user. Located inside the University of Reykjavik, the group is just outside of the downtown area in South Reykjavik. With only four hours of light this time of year, I wasn’t able to get a good look at the university but the buildings I saw were pretty with huge glass walls.

If you have never considered looking up a local hackerspace on your vacation or business trip, I would strongly recommend you consider it next time. It’s a great way to meet like-minded folk in different locations.

from on January 7th, 2015Comments0 Comments